An image forming apparatus uses high voltages such as, as is known, a transfer voltage. Furthermore, it is also known to control the duty ratio of a PWM signal so that the duty ratio increases in a stepwise manner and thereby gradually start up the transfer voltage.
However, due to various factors such as an inflow current into a transfer electrode, an hFE of a transistor, and a time of smoothing the PWM signal, a start-up time of the high-voltage power delays. This can cause insufficient target transfer output when the sheet has reached the image forming position, which results in lower image quality of the printed matter. On the other hand, in a case where a larger PWM value is applied from the beginning of starting the high-voltage power, the delay in the start time can be reduced. This, however, can cause overcurrent.
Thus, there is a need for an image forming apparatus that can reduce generation of overcurrent while suitably reducing delay in the output response of the output signal with respect to image formation.